From the past, a pump driving apparatus is proposed which drives a motor based upon a command value using discharge pressure—discharge flow characteristic and carrying out feedback of the discharge pressure, and drives a pump using the motor.
FIG. 1 is a block diagram illustrating a conventional pump driving apparatus.
The pump driving apparatus comprises a converter section 101, an inverter section 102, a motor 103, and a pump 104.
The converter section 101 receives an alternate current power source as input and generates a direct current voltage.
The inverter section 102 receives the direct current voltage as input and outputs an alternate current voltage.
The motor 103 is supplied the alternate current voltage.
The pump 104 is connected to an output shaft of the motor 103.
The pump driving apparatus also comprises a horse power command generation section 105, a subtraction section 106, a proportional controller 107, an integral controller 108, an integrator 109, an addition section 110, a speed control section 111, and a current control section 112.
The horse power command generation section 105 generates a horse power command based upon discharge pressure—discharge flow characteristic (hereinafter, referred to as P-Q characteristic), a current pressure, and a current flowing amount, the P-Q characteristic being generated, as is illustrated in FIG. 5, by a set pressure, a set flowing amount, and a set horse power defined for a predetermined power voltage.
The subtraction section 106 calculates a difference between the horse power command output from the horse power command generation section 105 and a current horse power.
The proportional controller 107 receives the horse power difference as input, and carries out the proportional control.
The integral controller 108 receives the horse power difference as input, and carries out the integral control.
The integrator 109 integrates the integral control result.
The addition section 110 adds the proportional control result and the integration result so as to obtain a proportion-integration control result (speed command).
The speed control section 111 receives the speed command as input, carries out the speed control operation, and outputs a current command.
The current control section 112 receives the current command and a DC voltage of the converter section 101, carries out the current control operation so as to generate a duty command, and supplies the duty command to the inverter section 102.
The pump driving apparatus further comprises a speed detection section 114, a flowing amount detection section 117, a pressure sensor 115, and a horse power operation section 116.
The speed detection section 114 receives a pulse output from a pulse generator 113 which is connected to the motor 103, and calculates a current speed of the motor 103 based upon a pulse interval.
The flowing amount detection section 117 receives the current speed as input, and calculates a discharge flow by taking a pump volume and the like into consideration.
The pressure sensor 115 detects a current pressure of discharge fluid from the pump 104.
The horse power operation section 116 calculates a current horse power based upon the current flowing amount and the current pressure.
Therefore, adequate pump control can be realized in which the defined P-Q characteristic is determined to be a maximum area.
However, a power voltage is not guaranteed to be kept to a predetermined voltage. A power voltage affects driving, stopping, and the like of adjacent apparatus and the like, and varies accordingly. Therefore, sufficient capacity cannot be realized when a pump is driven using P-Q characteristic which is defined for the predetermined power voltage.
Description is made further.
When a power voltage becomes lower than a predetermined rated voltage, a discharge pressure which is actually possible to be output becomes lower than the discharge pressure {circle around (1)} for the predetermined rated voltage, as is illustrated with {circle around (3)} in FIG. 2. This P-Q characteristic can be converted to torque—revolution speed characteristic of a motor (refer to FIG. 3). And, {circle around (1)}{circle around (2)}{circle around (3)} in FIG. 2 correspond to {circle around (1)}{circle around (2)}{circle around (3)} in FIG. 3, respectively. As a result, a condition continues where a current value does not reach for the command value corresponding to the P-Q characteristic illustrated with {circle around (1)}. And, for this time period, the integrator 109 of the P-Q control continues the integration, therefore, the discharge pressure greatly overshoots after the integration result exceeding the constant horse power region (windup phenomenon).
Therefore, in the past, the P-Q characteristic is determined, as is illustrated with {circle around (3)}, for not causing problem in control response even when a power voltage is lowered to some degree. As a result, a disadvantage arises in that a motor capacity cannot be utilized sufficiently.
On the contrary, when the discharge pressure which is actually possible to be output becomes higher than the discharge pressure {circle around (1)} for the predetermined rated voltage, as is illustrated with {circle around (2)} in FIG. 2, the output following the P-Q characteristic illustrated with {circle around (2)} becomes possible. However, a command value only corresponds to the P-Q characteristic illustrated with {circle around (1)}, therefore, a disadvantage arises in that a motor capacity cannot be utilized sufficiently, similarly.